Review of the Draft Fourth National Climate Assessment (2018) / Chapter Skim
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Appendix A: Comments on Appendix 5: FrequentlyAsked Questions
Appendix A: Comments on Appendix 5: FrequentlyAsked Questions
Pages 123-138
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From page 123... ...
For the FAQs that relate to specific draft NCA4 content, the provided information is generally consistent with the main text and it is useful when the main text is referenced. However, the emphasis and specific information sometimes differs between the FAQs and the main text.
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From page 124... ...
How is recent global warming different than warming in the past? The supporting text for this FAQ implies that only warming epochs have been linked with orbital cycles, while attributing cooling epochs specifically to volcanic eruptions.
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From page 125... ...
Orbital variations do not change the total amount of sunlight reaching the earth over the course of a year, but they affect its distribution by season and latitude, which then drive the growth or decay of high-latitude ice sheets and the strong positive climate feedback loops that go with them. The literature on this topic should be revisited by the draft FAQ authors to ensure the state of knowledge is accurately conveyed and the text should be revised to clarify the relationship between orbital cycles and both warming and cooling periods.
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From page 126... ...
The supporting text could indicate that the molecular structure of greenhouse gases causes them to absorb terrestrial infrared radiation (unlike N2 and O2, the most abundant gases in the atmosphere)
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From page 127... ...
On page 1456, lines 9-10 the FAQ response states, "water vapor cannot be the driver of global warming." One might argue that water vapor actually is a driver of global warming, since it is the dominant greenhouse gas. The point the FAQ authors may be trying to convey is that humans have no direct control over how much water vapor is in the atmosphere, although there is a strong indirect influence since evaporation and water vapor holding capacity increases with temperature.
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From page 128... ...
This FAQ response is generally accurate, but the authors should consider that 300-year records have their own issues and are not by themselves adequate to measure global surface temperature warming. Even though this FAQ does not explicitly say that these long records have more power than they actually do, it could be inferred from the text.
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From page 129... ...
This FAQ response emphasizes that warming will continue, but it depends on the emission scenarios, and precipitation will also increase, with wet areas getting wetter and dry areas getting drier, and heavy precipitation will be more frequent. These are all key points to convey and easily understood by the intended audience.
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From page 130... ...
On page 1467, line 20, "climate sensitivity" should be defined for the audience or replaced by a less technical explanation such as "differences in how climate responds to doubling of greenhouse gas concentrations." Line 13 on page 1467 could be misleading. The phrase, "different models produce slightly different projections of change," is only accurate when referring to global mean change, but audiences tend to think about climate change in terms of regional changes, so they may be misled to think that different models produce slightly different projections of regional change.
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From page 131... ...
Some plausible scenarios of future greenhouse gas emissions would have global surface temperature increasing by 4-9oF by 2100. Scientists think that warming in excess of 3.6oF (2oC)
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From page 132... ...
Revised wording that could be used is, "Conversely, it is also possible for several types of extremes to occur close to the same time (e.g., a sequence of hot days that occur during dry conditions that make both worse; or several rainfall events occurring one after another that, taken together, produce flooding) that may not be considered extreme individually, but may cause." Does global warming affect extreme weather?
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From page 133... ...
Since the effect of a single wind farm would be marginal relative to global carbon emissions, the economic value of that action can be estimated as the product of an estimate of the social cost of carbon times the reduction in carbon emissions from fossil fuel sources. What is the difference between climate change mitigation, adaptation, and resilience?
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From page 134... ...
On page 1487, lines 22-29, it is important to emphasize that solar radiation management does not reverse global warming caused by the presence of carbon dioxide and other greenhouse gases in the atmosphere (which is what the question asks)
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From page 135... ...
In fact, much of the focus is on warming oceans eating away at the place the ice sheets go afloat in West Antarctica. A balanced statement is needed on how both warming air temperature that will make more meltwater and warming ocean could make this ice sheet collapse rapidly.
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From page 136... ...
On page 1494, lines 19-20, it would be useful to highlight corals as an especially vulnerable habitat-forming species. How do higher carbon dioxide concentrations affect plant communities and crops?
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From page 137... ...
. Higher atmospheric carbon dioxide concentrations allow plants to photosynthesize more with lower water losses and higher water use efficiencies.
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From page 138... ...
The high levels of fire in these forests results from a combination of extreme weather events as well as the lasting effects of fire suppression, past logging, grazing, and invasive species in building up fuel loads. Large, high-severity fires convert unnaturally dense and structurally homogeneous dry forests to non-forest ecosystems in many places, with attendant loss of ecosystem services (Schoennagel et al., 2017)
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